The present invention relates to an in-process gage and in particular to a gage employing flexible linkages supporting a bellcrank to transfer workpiece size information to the electronic gaging transducer enabling the workpiece size information to be used to control the machining process.
High precision machining operations, such as the grinding of the crank pin journals of a crankshaft, is accomplished with an in-process gaging system in which the part size is measured during the grinding process. Information regarding the part size received from the gage is used to control the grinding process. Due to the high precision required of the grinding operation, the gage must also be of high precision.
When precision grinding the crank pin journals of a crankshaft, the small clearance between the throws and the counter weights on opposite sides of the shaft from the journals requires a thin gage to fit into this extremely narrow operating envelope. The moving parts of the gage, which must fit within a sealed case, must be narrower still. To develop a gage head which fits into extremely small spaces, it is generally not possible to use a pivot shaft with preloaded anti-friction bearings as has been done in the prior art for larger precision gages.
It is an object of the present invention to provide a gage for in-processing measuring of a workpiece having a narrow or thin gage head to fit into small spaces.
The gage head of the present invention utilizes a four bar linkage system in which the floating bar of the linkage is in the form of a bellcrank having one arm extending through the gage casing. An active feeler is coupled to the bellcrank arm and engages the workpiece surface. A fixed feeler is attached directly to the body of the gage head. Movement of the active feeler to stay in contact with the workpiece surface results in motion of the bellcrank relative to the gage body. This relative motion is transferred to an electronic position sensing transducer, producing an electrical signal related to the workpiece size that is used in controlling the grinding process.
The bellcrank pivot provides precise rotation of the active feeler with virtually zero back lash. This is necessary for a high precision gage. The actual center of rotation of the bellcrank is located near the edge of the gage casing. By being so situated, the casing is easily sealed where the bellcrank passes through the casing in spite of the extremely limited clearance provided in a gage of small size.